Append parent contexts to subtodo

This works identically to append_parent_projects option. Code was
generated by simply `s/project/context/`

topydo.conf

@@ -28,3 +28,5 @@ ignore_weekends             = 1
 [dep]
 ; Add parent projects when adding sub todo items
 append_parent_projects      = 0
+; Add parent contexts when adding sub todo items
+append_parent_contexts      = 0

topydo/lib/Config.py

@@ -61,6 +61,7 @@ class _Config:
 
             # dep
             'append_parent_projects': '0',
+            'append_parent_contexts': '0',
         }
 
         self.config = {}
@@ -148,6 +149,12 @@ class _Config:
         except ValueError:
             return self.defaults['append_parent_projects'] == '1'
 
+    def append_parent_contexts(self):
+        try:
+            return self.cp.getboolean('dep', 'append_parent_contexts')
+        except ValueError:
+            return self.defaults['append_parent_contexts'] == '1'
+
     def _get_tag(self, p_tag):
         try:
             return self.config[p_tag]

topydo/lib/TodoList.py

@@ -141,6 +141,15 @@ class TodoList(TodoListBase):
                 for project in p_from_todo.projects() - p_to_todo.projects():
                     self.append(p_to_todo, "+{}".format(project))
 
+        def append_contexts_to_subtodo():
+            """
+            Appends contexts in the parent todo item that are not present in
+            the sub todo item.
+            """
+            if config().append_parent_contexts():
+                for context in p_from_todo.contexts() - p_to_todo.contexts():
+                    self.append(p_to_todo, "@{}".format(context))
+
         if p_from_todo != p_to_todo and not self._depgraph.has_edge(
             hash(p_from_todo), hash(p_to_todo)):
 
@@ -155,6 +164,7 @@ class TodoList(TodoListBase):
             self._depgraph.add_edge(hash(p_from_todo), hash(p_to_todo), dep_id)
             self._update_parent_cache()
             append_projects_to_subtodo()
+            append_contexts_to_subtodo()
             self.dirty = True
 
     def remove_dependency(self, p_from_todo, p_to_todo):